Field of the Invention
Embodiments of the present disclosure relate generally to power conversion and, in particular, to regulating output power of a power conversion module.
Description of the Related Art
Solar panels, or photovoltaic (PV) modules, convert energy from sunlight received into direct current (DC). The PV modules cannot store the electrical energy they produce, so the energy must either be dispersed to an energy storage system, such as a battery or pumped hydroelectricity storage, or dispersed by a load. One option to use the energy produced is to employ one or more inverters to convert the DC current into an alternating current (AC) and couple the AC current to the commercial power grid. The power produced by such a distributed generator (DG) system can then be sold to the commercial power company.
In order to mitigate potential safety hazards, a DG coupled to a commercial power grid must be operated in accordance with relevant regulatory requirements, such as IEEE-1547. As part of meeting the IEEE-1547 requirements, an inverter within a grid-coupled DG must shut down under certain circumstances, such as line voltage operating outside of pre-defined limits.
In some DGs, inverters may be installed in a string configuration as part of power conditioning units (PCUs) coupled via an AC bus to the grid, where each PCU comprises a PV module coupled to an inverter. Based on wire gauge and distance from the grid, a voltage increase may be seen along the string, with the highest voltage level generally at the PCU farthest from the grid. As a result of such voltage increase along the string, utility voltage fluctuations that are within specifications as seen at the grid may result in a voltage at one or more of the inverters, in particular the inverters located at the far end of the string, that exceeds specifications and causes the impacted inverters to shut down for a required time period. Further, in an inverter that uses a mechanical relay for isolation from the AC bus, the relay will open. As the impacted inverters cease power production and thereby cause the voltage along the string to drop, the inverters may reactivate, begin producing power and couple such power to the grid by closing the corresponding relay, resulting in a continued oscillation that negatively impacts power production as well as causes relay “chatter” that potentially shortens the life of the inverter isolation relay.
Therefore, there is a need for a method and apparatus for efficiently regulating output power from a power conversion module.